This behaviour is controlled by the output style you are using. You can either use an output style that is preset to generate individual numbers for each reference, or edit the output style you are using, to change this setting, and save as to a new name, and use that new style in the word manuscript on the Endnote ribbon (if Word 2007, 2010 or 2013) or in the format bibliography dialog (all other versions of Word). ACS has the combine option selected, so you would (in endnote) Edit, Output styles> edit “ACS” and under the citation settings, chose Numbering, and untick the box as in the attachment.
then save as to a new name - and go to your word document as described above - change to this new output style. – you may need to “Select another Style” if the new file name is not in the list yet.
